A Constant Volume Sampler (CVS) compatible auto exhaust particulate sampling system has been built and successfully operated. The system can be used to sample exhaust isokinetically at constant temperature, yields internally consistent results, and can be operated conveniently and frequently.Studies with the sampling system have shown that vehicles equipped with oxidation catalysts convert some of the sulfur in the gasoline to sulfuric acid containing particulates. Bound water was shown to be a major component of the sulfuric acid exhaust particulate. Catalyst type and system design are believed to have a marked effect on the sulfuric acid conversion with additional research required to determine what features result in lower sulfate emissions.Emission tests have shown that platinum emission rates are lower than 2 × 10-5 g/mi. More sensitive analytical techniques will be required to obtain information on a more quantitative basis. Short term tests with NOx reduction catalysts have shown that the catalyst attrition rates can be readily measured.